I sent my plumber in before we closed to stem the damage.On top of that the subfloor in the bathroom, and hallway just outside it, on the main level will need to be replaced as a consequence of pets urinating in that location for years - when we bought the property, the moisture readings in that area were off the charts, it was only later we figured out why.

He says there has been un-handled moisture damage in the bathroom and the kitchen countertop needs to replaced, I know it true ( showed up in the property inspection) . 

So I'm thinking quarterly would be viewed as generally acceptable in my area, even though it is not a common practice in my experience.I'm probably going to phrase the inspections as geared towards identifying any potential leaks (pipes, windows), moisture issues, etc, to protect the tenant's home, and ensure it stays safe and healthy for them and their family.

Penetrations may not have been properly flashed.

I’ve had people come inspect the crawlspace for leaks, spray for mold, and installed increased ventilation in the bathrooms to cut down on moisture.

Tenant agrees to allow Landlord timely access to premises to do maintenance and repair.Tenant will notify Landlord in a timely manner of any damages or problems as they arise, including damages caused by Tenant, malfunction of appliances or fixtures, and water/moisture leaks and spots.Tenant will take care of the premises, keeping them clean and clear of debris.

This takes the moisture out of the heat, recirculates into the building envelope, and brings fresh air in.

The heat somehow causes the pipe to sweat from moisture in the air.

Moisture conditions:  Will this product deteriorate or rust due to moisture in the space?

Even skylights in perfect condition are often installed with incorrect flashing, which is the metal that diverts water away from the penetrations in your roof (where roofs meet walls, chimneys, roof valleys, etc).